Photographic elements exhibiting reduced haze and method for preparation



United tates atent O PHOTOGRAPEC ELElviENTS EXHEITING RE- ?KEJBCED HAZE AND METHQD FGR PREP- Beat Meerkamper, Red Bank, and Jacob Quentin Umberger, Holmdel, NJ, assignors to E. I. du Pont de Nemours and (Iompany, Wilmington, Del, a corporation of Delaware No Drawing. Filed Dec. 11, 1959, Ser. No. 858,865

- 5 Claims. (Cl. 9667) This invention relates to photographic elements comprising a support coated with a gelatino-silver halide emulsion containing an agent for increasing the covering power of the developed silver. This invention more particularly relates to a method of improving such photographic elements by increasing the speed and improving the clarity and reducing the turbidity of the processed emulsion layers containing poly-N-vinyllactams as covering power increasing agents.

The use of poly-N-vinyllactam covering power increasing agents in gelatino-silver halide emulsions is disclosed and claimed in assignees copending application of Overrnan et al., U.S. Ser. No. 748,605 filed July 15, 1958, now abandoned. As shown in that application, the presence of the compounds disclosed therein increases the efficiency of the silver halide in the system. This efficiency manifests itself by increases in efiective speed, contrast or gamma. Such increases in silver halide efficiency are much to be desired in certain types of photographic elements such as films for radiological use and films for use in the graphic arts field.

However, the use of such agents in gelatino-silver halide emulsions systems produces photographic emulsions which show a tendency toward turbidity or haziness in the coated and processed emulsion layer which is undesirable and in turn causes undesirable eifects on definition.

The use of gelatin antiabrasion coatings over gelatinosilver halide emulsion layers is very old in the art and such layers are generally coated in such a manner as to give a dry coating weight of not more than milligrams per square decimeter. It is known that heavy gelatin abrasion layers, e.g., up to 10 milligrams per square decimeter, are necessary in the case of X-ray emulsions because of the greater susceptibility of such emulsions to abrasion.

Further, it is known to use poly-n-vinyllactams as the sole binder for photographic silver halide emulsions. It is also known to add polyvinyl pyrrolidone and copolymers thereof to gelatino-silver halide emulsions to overcome yellow fog. In addition it is known to add polyv nyl pyrrolidone to gelatino-silver halide emulsions or to image receptive layers for use in the so-called inverse transfer process. In this latter case it is used in quantities up to 40 parts or more per 100 parts of total binder to produce a turbid or non-homogeneous layer when the emulsion is coated and dried. The non-homogeneity is for the purpose of lowering the cohesiveness of the emulsion layer and the receptive layer during the inverse transfer process. X-ray emulsions can also be used in this inverse transfer process. However, no art is known where gelatin layers so heavy as to be outside the category of antiabrasion layers have been coated over emulsions containing covering power increasing agents.

An object of this invention is to provide photographic elements which have reduced haze and methods for their production. A further object is to provide such elements, which have reduced haze despite the use in the photographic emulsions of poly-N-vinyllactam covering power increasing agents, and methods for production. A still further object is to provide such elements which result in improved sensitometric characteristics and methods for their production. hereinafter.

These and other objects have been quite unexpectedly accomplished by the following invention which comprises a method for producing photographic elements having reduced haze which comprises coating a macromolecular polymeric base support with a layer of photographic emulsion containing poly-n-vinyllactam covering power increasing agent, and coating a heavy layer of gelatin thereover in sufficient quantity to reduce the haze in said element. The heavy gelatin layers not only reduce haze to acceptable levels, but, as a consequence, such layers increase the resolution of the resulting photographic elements. Most surprisingly, the heavy gelatin overcoatings produce increased photographic speed.

in general, it has been found that a coating weight of from 20 to 40 milligrams of gelatin based on dry weight per square decimeter is quite efficacious in producing the advantageous elfects of the invention. The gelatin solutions for coating the heavy overcoating layers may vary in concentration over a wide range but, in general, a concentration of from 3 to 10% will be found to be suitable. In addition, the heavy overcoating layers provide an improved degree of gloss, possibly associated with the emulsion speed increase, to the surface of the coated element when viewed by reflected light. This becomes reasonable when it is realized that 20 mg./dm. of gelatin is equivalent in thickness to 1.6 microns of AGBr, the average particle size of high-speed emulsions such as are employed in medical X-ray films. The method of applying the relatively heavy gelatin overcoating is not too critical and the emulsion layer may be overcoated in the wet or dry state. There is, however, a somewhat greater reduction in haze when the emulsion is overcoated Wet. This is of considerable importance because in the manufacture of overcoated photographic elements as it is now sometimes carried out, antiabrasion layers are applied successively to freshly coated emulsion layers while the latter are still wet. The haziness in the dried emulsion layers coated from emulsions containing the covering power increasing agents noted above is of course, caused by light scattering in the emulsion 'and/ or at the emulsion/ air interface. Therefore, the haze may be measured by determining the amount of scattered light when passing through any particular film from which the silver halide has been removed by fixation. It is preferable to make the haze determination on unexposed and undeveloped films since the fog/ silver deposits also scatter light. The haze measurements in the following examples were made on undeveloped samples and are therefore independent of the fog level. The measurements were made on a Lurnetron Model 402E photoelectric colorimeter sold by the Photovolt Corpora- Other objects will appear 0 tion, Madison Avenue, New York 60, New York.

As a means of interpreting the figures derived in measuring the films of the examples, the following standard values for haze are given which are relative numbers indicating the fraction of light that is scattered through the film:

0-6 clear 6-15 detectable (not noticeable on light box viewing) 15-40 transparent haze 40+ milky or turbid The invention will now be illustrated in and by the following examples.

EXAMPLE I 3 It was digested with an organic sulfur compound and gold chloride. After digestion, 36.4 grams per mole of silver halide of poly-N-vinyl-2-pyrrolidone (PVP) having a molecular weight of approximately 45,000 was add- 4 EXAMPLE II A gelatino-silver iodobromide emulsion was made as described in Example I and sixteen emulsion coatings were made, eight of which were overcoated to give a dry ed glve of l i totalt j The 5 coating weight of mg./dm. from a 3% aqueous gelaf g emu a? i coa e 5 S P 0 tin solution and eight others were overcoated to give a ventfon Ysub 6 P u ,fil an i fi dry coating weight of 30 mg./dm. from a 9% aqueous to g a dry coatmi i t 0 Th m1 O s ver gelatin solution. The aqueous gelatin overcoating soluhahde P Square eclfneter' e coae ms were tions contained varying amounts of chrome alum and in 111 a cPnvcntlonal manner- 9 coated film 10 dimethylolurea hardening agents as indicated in the tawasovercoated with a 3% aqueous gelatin SQhulOH conbis. Haze, was m.easured on the fixgd, washed and drqed ta g milligram of 911F011}? all-1m and 1311111 films. sensitomeric data were obtamed on films wh1ch gram of dlmethylol urea P mlulgfam 0f gelatlfl- The had been exposed to a low intensity X-ray exposure and dry coating weight of the overcoating was 10 milligrams rocessed as described in Example I. The results are per square decimeter. The other coated film was overshown in the following table.

TABLE I Hardener Sensitometry Coating Number Coating Dimeth- Weight Chrome ylol Over- Haze Speed Gamma Fog Gelatin, Alum Urea, Coated Dry (RelamgJdmJ mg./dm. mg./dm. tive) 10 0. 2 None 33 159 2. 7 07 10 0.2 None 29 142 2.5 .14 10 0.2 0.3 30 154 2.2 .07 10 0.2 0.3 29 156 2.1 .11 10 None 0.3 27 152 2.1 .05 10 None 0.3 127 2.2 .12 10 None None 26 164 2. 3 07 10 None None 28 143 2. 3 12 30 None None 11 177 2. 1 07 30 None None 13 150 2. 3 15 30 None 0.3 13 177 2.0 .06 30 None 0.3 13 153 2.1 .17 30 0.2 0.3 11 194. 2.1 .06 30 0. 0.3 11 152 2.2 .14 30 0.2 None 11 174 2.2 .07 30 0.2 None 12 142 2.3 .17

coated with a 9% aqueous gelatin solution containing about 0.007 milligram of chrome alum and about 0.01 milligram of dirnethylol urea per milligram of gelatin. The dry coating weight was 30 milligrams per square decimeter. These two films were dried in a conventional manner. The two films were exposed to low intensity X-rays in the presence of an intensifying screen through an aluminum square root of two step-wedge according to a procedure based on the American Standard Method for the Sensitometry of Medical X-Ray Films-Pb 2.9 1956. The exposed coatings were developed for 5 minutes in a developer having the following composition:

The coatings were then fixed, Washed and dried in a conventional manner. Results of sensitomeric tests for speed, gamma and fog for all tests are given below. Speed is given in terms of reciprocal of exposure at a density of 0.7. Haze measurements are relative numbers described above.

Law Intensity Exposure Coating Speed Gamma Fog Dry (Relative) Haze 10 mgJdIn. 390 3. 08 O8 19. 8 30 mg./dm. 410 3. 8O 07 8.0

It will be noted that there was a significant reduction in haze Where the heavy gelatin overcoating was used and also that the sensitomeric characteristics were either unaffected or improved.

It will be seen from the above examples that significant improvements in haze are brought about by the use of heavy gelatin overcoatings on emulsion layers containing covering power increasing agents. It will further be seen that such heavy gelatin overcoatings do not have any detrimental effect on the sensitomeric characteristics of the emulsion layers.

EXAMPLE III A gelatino-silver iodobromide emulsion was made as described in Example I and two coatings were made having a dry coating weight of 100.milligrams.of silver halide per square decimeter. The coated films were dried in the conventional manner and one coating was used as a control and not treated further. One coating was overcoated With a 3% aqueous gelatin solution containing 18 milligrams of formaldehyde per gram of gelatin of give a dry coating Weight of 10 milligrams per square decimeter. The other coating was overcoated with a 9% aqueous gelatin solution containing 18 milligrams of formaldehyde per gram of gelatin to give a dry coating weight of 30 milligrams per square decimeter. Haze was measured on the fixed, washed and dried films. Sen sitomeric data were obtained on films which had been ex posed to a low intensity X-ray exposure and processed as described in Example I. The results are shown in the following table.

Abrasion sensitomet Coating Coating, Haze Speed ry Weight (Relative) Gamma Fog It will be seen that the use of heavy gelatin abrasion overcoating decreases the haze to a considerable degree and that formaldehyde hardening does not interfere with the efiect. Sensitometric characteristics were also not detrimentally afiected.

The invention is not limited to photographic gelatinosilver halide emulsions of the silver iodobromide type. The invention may be applied to other gelatino-silver halide emulsions, e.g., gelatino-silver bromochloride emulsions of the lithographic type. The invention is also not limited to overcoating gelatino-silver halide emulsions containing poly-N-vinyl-2-pyrrolidone as the covering power increasing agent. Silver halide emulsions containing poly-N-vinylcaprolactam, poly-N-vinyl-S-methyl- 2-pyrrolidone and poly-N-vinylpiperidone may also be beneficially aided by the heavy gelatin overcoatings of the invention. The invention is particularly efficacious with photographic emulsions whose grain size is relatively large. The emulsions to be overcoated may contain any of the well known optical sensitizing dyes as well as non-optical sensitizers such as sulfur sensitizers containing labile sulfur, e.g., allyl isothiocyanate, allyl diethyl thiourea, phenyl isothiocyanate and sodium thiosulfate; the polyoxyalkylene ethers disclosed in Blake et al., US. Patent 2,400,532 and the polyglycols disclosed in Blake et al., US. Patent 2,423,549. Other non-optical sensiitzers such as amines as taught by Staud et al., US. Patent 1,925,508 and metal salts as taught by Baldsiefen US. Patent 2,540,085 and Baldsiefen et al., US. Patent 2,540,086 may also be used. Antifoggants, e.g., benzotriazole, triazaindenes and the phenolic antifoggants disclosed in assignees copending application, Forsgard, US. application Serial No. 757,460 filed August 27, 1958, may be used. Any of the usual film supports of macromolecular polymeric materials may be used such as cellulose esters, e.g., cellulose triacetate, cellulose acetate/ butyrate; superpolymers, e.g., polystyrene, poly (vinyl chloride or vinyl acetate); polyvinyl acetals, e.g., formal and acetal; polyamides, e.g., polyhexamethylene adipamide, and polyesters, e.g., polyethylene terephthalate. The vinylidene chloride copolymer-coated oriented polyester films of Alles et al., US. Patent 2,627,088 are especially suitable.

The novel overcoating may be applied by any suitable means such as skim coating over the undried emulsion lawer as taught by Daily, US. Patent 1,699,349 and Dixon, US. Patent 1,892,484 or by the apparatus disclosed in assignees copending applications of Brandsma et al., Serial No. 849,376, filed October 28, 1959 and Beck, US. application Serial No. 506,458, filed May 6,

An advantage of the invention is that the heavy gelatin overcoating provides a simple method of taking full advantage of the new discovery of using covering power increasing agents to improve maximum density, contrast and effective speed of gelatino-silver halide emulsions.

Another advantage of the invention is that the heavy gelatin overcoatings can be applied by the ordinary technician with conventional apparatus. Since aqueous gelatin solutions are used, no volatile solvents are involved necessitating the use of solvent recovery systems. Conventional coating and drying equipment can be used to practice the invention.

What is claimed is:

1. A method for producing photographic elements having reduced haze which comprises coating a macromolecular polymeric base support with a layer of photographic gelatino-silver halide emulsion containing poly- N-vinyllactam silver covering power increasing agent and coating a layer of gelatin thereover of from 20 to 40 mg. of gelatin per square decimeter, based on dry weight.

2. A method for producing photographic elements having reduced haze which comprises coating a macromolecular polymeric base support with a layer of photographic gelatino-silver iodobromide emulsion containing polyvinyl pyrrolidone silver covering power increasing agent and coating a layer of gelatin thereover of from 20 to 40 mg. of gelatin per square decimeter, based on dry Weight, said gelatin being applied to said emulsion layer as an aqueous solution of from 3 to 10% gelatin by weight.

3. Method according to claim 2 wherein said emulsion layer is still wet when the gelatin layer is coated there over.

4. A photographic element having reduced haze comprising a macromolecular polymeric base support having coated thereover a photographic emulsion layer containing poly-N-vinyllactam silver covering power increasing agent, said emulsion layer having coated thereover an overcoating of gelatin in an amount of from 20 to 40 mg. of gelatin per square decimeter, based on dry weight.

5. A photographic element having reduced haze comprising a macromolecular polymeric base support having coated thereover a photographic gelatino-silver halide emulsion layer containing polyvinyl pyrrolidone silver covering power increasing agent, said emulsion layer having coated thereover an overcoating of gelatin in an amount of from 20 to 40 mg. of gelatin per square decimeter, based on dry Weight.

References Cited in the file of this patent UNITED STATES PATENTS 2,415,624 Brown et al Feb. 11, 1947 2,948,614 Allen et a1 Aug. 9, 1960 2,995,444 Dersch Aug. 8, 1961 FOREIGN PATENTS 609,826 Great Britain Oct. 7, 1947 687,751 Great Britain Feb. 18, 1953 OTHER REFERENCES Glafkides: Photographic Chemistry, vol. 1, Fountain Press, London, 1958, page 474, 

5. A PHOTOGRAPHIC ELEMENT HAVING REDUCED HAZE COMPRISING A MACROMOLECULAR POLYMERIC BASE SUPPORT HAVING COATED THEREOVER A PHOTOGRAPHIC GELATINO-SILVER HALIDE EMULSION LAYER CONTAINING POLYVINYL PYRROLIDONE SILVER COVERING POWER INCREASING AGENT, SAID EMULSION LAYER HAVING COATED THEREOVER AN OVERCOATING OF GELATIN IN AN AMOUNT OF FROM 20 TO 40 MG. OF GELATIN PER SQUARE DECIMETER, BASED ON DRY WEIGHT. 